Signal receiver



M. G. CROSBY l SIGNAL RECEIVER Jan. 2s, 1941. l

" Filed June 20. 1932 5 Sheets-S199?. 1

Jan. 28, 1941. M. G. CROSBY 252291540 vsmmu., RECEIVER Filed June 20. 1832 y 5 Sheets-Sheet '2 MURRAY a. cRosY supfnuermopvA/e Recs/vee A'ITORNEY Jn 2811941, M. e. cnosav y 2,22%640' SIGNAL RECEIVER lNvx-:NToR

MURRAY e. cRosY A'TTo'RNEY Jan. 28,1941- NLG; cRoslaYA 2,229,540

SIGNAL nncmrvsx Filed June '20. 1932 5 Shoots-Shet 4 for PNB '//5 /20 MURRAY G. fRosY l BY ATTORNEY Patented Jan. 28, 1941 UNITED STATES SIGNAL RECEIVER Murray G. Crosby, Riverhead, N. Y., assignor to Radio Corporation of America, a, corporation of Delaware Application June 20, 1932, Serial No. 618,154

Claims.

Certain novel fea-tures of the invention have been pointed out in the claims attached hereto. Other features are defined in my divisional application'Serial Nq. 323,077, filed March 9, 1940.

Some methods ofl carrying out the present invention and some forms of circuit arrangements by means of which said invention may be c-arried out will be described with reference to the drawings in which: v

Figure 1 shows diagrammatically a receiver devised according to and employing the principles of my present invention by means of which fre- 25 quency modulated signals may be demodulated;

Figures 2, 3, and 3a show modifications ofthe arrangement of Figure 1,;

Figures 4 and 5 show curves explanatory of the method of operating any of the receivers disclosed above when it is desired to receive phase modulated signals; i

Figures 6, 7, 7a, 8, 9, and 9a illustrate circuits which may be included in the frequency modulated signal receivers of the prior figures to adapt signals; o

Figure 10 shows the correction circuits of Figures 6, 7, 7a, 8, 9, and 9a incorporated with the frequency modulation receivers of Figures 1, 2, 3, vand 3a; while,

Figures 11 and 11a show diagrammatically other applications of the present invention.

` In Figure 1, I .indicates an aerial system connected with a signal amplifier 2. This signal amplifier may include one or more stages of thermionic radio frequency amplifiers. The unit 2 may also include an autom-atic volume control Where amplitude modulation is to be received. Where frequency or phase modulated signals are to be received the unit 2 may include a limiter device. Furthermore, the unit 2 may be a superheterodyne receiver which includes the features enumerated above or any combination thereof. All that isnecessary is that the frequency modu- 55lated signals appear without any alteration in them to efficient reception of phase modulated (Cl. Z-20) the lines 3 and 5 connected with the output of 2. A part of .the energy, that is, the frequency modulated signal appearing ln the output of lines 3 and 5 from the unit 2, is fed through a transformer 1, having a primary winding and a sec- 5 ondary winding 6, to a potentiometer resistance P1. A thermionic coupling tube A has its control electrode 9 connected with a movable point I0 on the potentiometer resistance P1 and its cathode l I connected through a biasing battery I2 .to the 10' lower terminal of the potentiometer resistance P1. Inthis m-anner the frequency modulated signals appearing in the transformer I are amplified or relayed in A and appear on the anode I3 thereof and are transferred therefrom to .the primary winding I4 of a combining transformer T.

Another portion ofthe frequency modulated energy appearing in the output of the unit 2 ls fed by lines I6 to the primary winding I1 of a transformer I8 having a secondary winding I9, theterminals ofwhich are connected to the input end of a transmission line L comprising series inductance I and parallel capacity C, which serve Y to filter the radio frequency signal to be demodulated and also serve, as will appear more in detail hereinafter, to effect the phase thereof and permit conversion of the frequency modulated signals into amplitude modulated signals. The output terminal of the line L terminates in a damping resistance R. The desired point along 30 the line L is connected by lead 20 to a potentiometer resistance P2. A .thermionic amplifier B has its control electrode 22 connected to the movable point 23 on the potentiometer P2 and its cathode 24 connected through a biasing source 25 35 to the lower potential terminal of P2. The anode -26 of thermionic tube B is connected to the cath'- vode 24 of tube B by Wlay of the primary winding I4 of the combining transformer T. Charging potential for the anode I3 of tube A 4 .and for the anode 26 of tube B is supplied from asource 28 connected in series between the cathode circuits I I and 24, both of which are grounded, and the an-odes I3 and 26 of tubes A and B respectively. A secondary winding 29 of transformer T impresses the combined signals on the control grid 30 and cathode 3l of a demodulatlng or rectifying tube RT. The control electrode of tube RT is biased to a characteristic at which complete demodulation takes place by means of 5 a biasing battery 32. The demodulated 'signals appearing o n the anode' 33 of tube RT may be impressed from a jack 34 in this circuit to any utilization means, as, for instance, telephones.

In Figure 2 all of. the energy relayed or ampli- 5 fled in the unit 2 is fed through the lines 3 and to the input transformer I8 of the long transmission line L. This line L is similar in some respects to the line L of Figure l, but differs therefrom in that this transmission line ls undamped, so that reflection takes place along the line. Thus the far end of the line may be either openy ended or short-circuited. The energy from this line is fed by lead 35, connected to a tap on line L, to the control grid 34 of tube A, and by line 31 to the control grid 361 of tube B so that energy may be impressed from different points on the line L to the control electrodes of the `two detectors A and B. The line L is grounded at'G, while the cathodes 44 of the tubes A and B are also grounded at G, as shown' to complete the input circuits of A and Bl. The control electrodes 34 and 36 are maintained at the desiredbiasing potential by means of a biasing source` 2| connected in series with the line L.

The anode electrodes 42 and 43 of tubes A and B respectively are connected to the primary winding of a combining transformer T, the

output winding 41 of which is connected with a utilization circuit. Charging` potential for the anodes 42 and 43 of tubes A and B respectively is supplied from a source 46 connected between a tap on the winding 45 and the cathodes 44 of the tubes A and B respectively. When frequency modulated signals are to bev received the anodes 42 and 43 of tubes A and B respectively are connected, as "shown, in push-pull relation. If amplitude modulated signals are to be received the anodes 42 and 43 of tubes A and B respectively are connected in parallel relation with the input winding of the combining transformer T.

In the modification shown in Figure 3 the frequency modulated signal appearing in the lines 3 and 5, connected withthe output of the unit 2, is divided into three parts. The first part is fed through a transformer 1 to the input of a transmission line L. 'I'he transmission line L is damped by a terminal resistance R in a manner similar to that in which the transmission line L of .Figure 1 is damped. A coupling tube A has its control electrode 9 connected to a movable point I0 on the inductance of the transmission line L. The anode I3 of tube A is connected to the primary winding I4 of a combining transformer T3.

A second portion .of the energy appearing in the lines 3 and 5, connected with the output of A2, is fed by means of lines I6 to the primary Winding I1 of a transformer I8, the secondary winding I9' of which is shunted by a potentiometer resistance P1. The energy appearing across P1 or a portion thereof is fed by means of a movable tap 23 to the control electrode 24 of a coupling tube B, the anode 26 of which is connected with the primary winding I4 of combining transformer T3. Charging potential for the anode I3 of tube A and anode 26 of tube B is supplied from a source 28. Biasing potential for the control electrode 9 of tube A is supplied from a source I2 connected to the line L and to ground G. Biasing potential for the control electrode 24 of tubeAB is supplied from a source 25 connected between the cathode and control electrode 24 of tube B. l

The third portion of the energy appearing in 'the lines 3, 5, connected with the output of the unit 2, is supplied by way of lines 30 to a coupling inductance 3| coupled with an inductance 32. 'I'he inductance 32 is in series with an inductance 33 connected with the control electrode 34 of a rectier tube C, and also in series with an inductance 35 connected with the control electrode 36 of a rectifier tube D. The inductances 33 and 35 form the secondary inductances of a transformer T1 having a primary winding 31, one terminal of which is connected to the terminal of the secondary winding 38 of transformer Ta and to the terminal of a shunting potentiometer resistance Pz, while the yother terminal of primary winding 31 is connected to a movable point 40 of the potentiometer P2. The anode 42 of tube C and arrode 43 of tube D are connected through windings 44 and 45 respectively of transformer ,T4 and through anode charging potential source 46 to the grounded cathodes of tubes C and D respectively. The secondary winding 41 of transformer T4 is connected with a utilization circuit. Biasing potential for the control electrodes of tubes C and D is supplied by a source 48 connected as shown.

In the modification shown in Figure 3a the receiver is similar in construction to the receiver of the modification shown in Figure 3, except. that energy is transmitted from the output lines 3 and 5 of unit 2 through two paths or in two parts only, one of which is impressed through the damped transmission line L on to the input electrodes of coupling tube A, and the other of which is impressed co-phasally through the inductance 32 on the input electrodes of the tubes C and D. In other words, in this modification the signal is divided into two parts only for transmittal through two paths, whereas in the modification shown in Figure 3 it was divided into three parts.

In operation, as will appear more in detail hereinafter, the receiver of Figure 3a follows very closely the operation of the receiver of Figure 1.

The operation of all of the receivers disclosed in the various modifications above to receive frequency modulated signals depends upon the fact that the electrical length of a filter or a transmission line, which consists of a series of sections composed of inductive, capacitive and resistive 'elements in a series and/or parallel arrangement or any one or a combination of said elements in said arrangement, varies with the impressed frequency.

` In the following explanation a transmission line will be utilized although it will be understood that a filter, such as a high pass, low pass, band pass, band elimination, etc., may be used. If the line is a given number of Wave lengths, long for a certain predetermined frequency, at a higher frequency the electrical length will be greater and at a lower frequency the electrical length lof the line will be less. The fact that this electrical length does change with frequency makes the phase at the output of the line changel with respect to that at the input of the line if the frequency of the signal transmitted by the line is varied.` Consequently, if the signal impressed on the input of the line is combined with the signal at the output of the line, an adjustment of the line may be made so that the phase difference between the voltage of the signal impressed on the input of the line and the voltage of the signal appearing on the output of the line increases as the degree of frequency modulation is increased. This phase difference will cause a variation in the amplitude of the resultant of the combined voltages so that an amplitude modulation is formed, which amplitude modulation is truly characteristic of the frequency modulation of the original signal. In accordance CFI .acteristcs; that isato say, they pass the carrier and side band frequencies in relatively unattenuated form to the detectors in which the outputs of the paths are combined and detected.

In particular, in the receiver of Figure 1 the frequency modulated energy appearing in lines v3 and 5 in the output of the unit 2 is fed directly through coupling tube A to the combining transformer T. Simultaneously energy from 2 appearing in lines 3 and 5 is fed by way of lines I6 to transformer I8 and to the transmission line L. A lead 20, connected to a movable point on the line L, transfers energy in the proper phaseto the potentiometer P2, from'whence the energy is' supplied tothe coupling tube B. The output energy from the line L, adjusted to the proper phase by means of the sliding tap 20, or similar means, is fedi` through the coupling tube B to the combining transformer T. The above transformer T, therefore, .is energized by energy from A and from B.

In operation, as the frequency of the carrier changes with modulation, the energy appearing in tube B and in particular in` the output circuit thereof, changes more rapidly in phase or in frequency than that from tube A, and a phase difference-betweenthe respective energies results` from coupling tube A and tube B. This change in phase of the energies from the two coupling tubesl results in a change in amplitude of the energy in the output circuits of the tubes A and B and in the primary winding I4 of transformer 'I'. This amplitude change or modulation is impressed on the input circuit of detector tube C and the demodulated signal appears in the output circuit thereof, from whence it may be utilized.

While this receiver of Fig. 1 has been illustrated as having a damped transmission line, it will be understood that in this receiver the transmission line L may be undamped, or open circuited at the end. In this case the tap is moved to a point on the line where the reflected wave cancels the incident Wave. The operation of this modified receiver will be apparent from the description of the receiver'of Fig. 3 which will be given after` a description of the .operation of the receiver of Figure 2.

In thereceivery of Figure 2, instead-of combining the energy from the output of the line L with that of the input of the line L, use is made of the fact that when the line L is open or short'- circuited at the far end, a reflection of signal energy transmitted by the line occurs along lthe line. The combination of this refiected energy with the incident energy.1.esults i'n combined' energy, the amplitude of which varies since the phase of the combined energies varies in the same manner as the phase of the energies combined by the coupling tubes A and B of Fig. 14 varies. When the signal frequency is changed with signal modulation a phase difference between the incident and reflected waves of line L is caused such that their resultant amplitude changes. Consequently. amplitude modulation of .the energy in the line at different points.

therealong is effected. Byv obtaining the output from the line L at two different points by way of leads 35, 31, `connected-at points such that at one point the incident and reflected waves are .combinedto increase the resultant, while at the other point two waves are combined to decrease the resultant two separate waves, with their modulationvenvelopes 180 out of phase. may be obtained; These two waves may be, and are, applied, as shown, to the d ilferential detectors A and B by Way'of leads 35 and 31 respectively. The detected output appearing on theanode 42 of A is 180 out of phase with respect to the detected output appearing on the anode 43 of tube B. This necessitates theuse of a push-pull transforner T connectedl to the outputs of tubes A and B. I'he demodulated signal may be utilized in circuit 4T. Where this receiver is used to receive amplitude modulated signals the output electrodes 42 and,43 of demodulators A and B respectively must be con` nected in-parallel relation so that the amplitude changes add rather than oppose each other.

The receiver of Figure 2, in addition to the advantage inherent in the receiver as described `in Figure 1, hasvan added advantage which is that the differential detectors employed in the output produce a cancellation of distortion resulting from square law detection and consequently a reduction of noise appearing with the the receiver of Fig. 3a will therefore be given rst.

l The receiver of Fig, 3a operates 'in a manner similar to the manner in which the receiver of Fig. 3 operates. In` Fig. 3a, however, the differential detectors C and D are fed by means of a` transformer T2 co-phasally bysignal energy from the output of the unit 2 appearing in lines 3 and 5 and in phase opposition by way of transformerl T1, the input of which is connected with the output of the coupling tube A, which in turn has its input circuit connected to a point on transmission line L. This combination makes the resultant amplitude modulations, fed to the detectors C and D over the two different paths, 180 out of phase.-` By means of the push-pull output transformer T4, connected with the anode circuits of C and D respectively, the rectified energies appearing in the output circuits of C and D are combined in proper phase when frequency modulation is received.

'I'he receiver illustrated in Figure 3a has all of l A ing the outputs of tubes C and D in push-pull relation or in parallel relation. Switch 46 enables this change in connection to be accomplished very readily.- The differential detector gives the consequent cancellation of square law detector distortion and noise reduction.

In the modification in Figure 3a. the frequencyv modulated signal appearing in the lines 3 and 5 is transferred to the combining transformers over two channels or paths.

In other Words, in Figure 3a one path, from the unit 2 to the detector system C-D, in-

5 cludes transmission line L, coupling tube A and transformer T1. This path has a fiatamplitude versus frequency characteristic, and freely passes all of the received signal frequencies including the carrier so that energy of side and carrier frequencies are impressed upon the secondary of transformer T1 from the primary of T1 in relatively unattenuated form. The secondary 33 of transformer T1 feeds Waves received from the primary of T1 in phase opposition to like input electrodes of the detector or rectifier systems CD. 'I'he effect of the transmission line upon the waves impressed on this path, as before explained, is to introduce shifts in phase in the wave output of the path, which shifts vary in accordance with the frequency of the waves applied to the input end of the line.

The other path, comprising conductors and transformer T2, also has a fiat amplitude versus frequency characteristic for the desired signal.

25 This other path, as is apparent from its construction, passes, from unit 2 to the detectors C-D, all of the received signal frequencies, including the carrier and side frequencies, without discrimination and with substantially no phase shift 3o or with substantially the same constant phase 1 shift over the entire received band of frequencies.

This latter path feeds waves from unit 2 through secondary 32, connected as shown to a point electrically intermediate the ends of secondary 33,

cophasally or in push-push to like electrodes of the detectors C-D.

The outputs of the two paths when combined produce a resultant which varies in amplitude. 'I'his resultant is detected by detector action of 40 C-D to reproduce the transmittedv audio, voice, or

Yother transmitted signal.

In the arrangement shown in Figure 3 the frequency modulated energy appearing in the lines -3 and 5 is transferred to the input electrodes of the detectors C and D over three different channels. A portion of the signal goes by way of transmission line L and coupling tube A to transformer T by'way of transformer Ta'. Another portion of the signal appearing in lines 0 3 and 5 goes by way of coupling tube B and transformer T; to coupling transformer T1 while a third portion of the signal appearing in lines 3 and 5 goes by way of line 30 to transformer T2 to excite the input electrodes of C and D cophasally, Also in Figure 3'the transmission line L and the coupling tubes are adjusted so that when the carrier is unmodulated the energy: from the output of the line L reaching the primary winding Il of combining transformer Ta exactly 00 cancels the energy reaching the winding Il of combining transformer Ts by way of tube B. Conf'sequently transformer T1 receives energy from coupling tube A and coupling tube B only when the signal is modulated. This energy from T1 adds with the energy from 'r2 on the grid or control electrode of one of the tubes C and D, and subtracts from the energy appearing from transformer T2 on the-control electrode of the other tube C or D. Consequently a differential action v takes place on the input electrodes of the tubes C and D and likewise a differential detector output action appears on' the output circuits of tubes C and D. 'I'he energyappearing on the anode of tube C is out of phase with respect to the 76 energy appearing on the anode of tube D and,

since the output circuits of these tubes are connected with a push-pull transformer T4, a resultant signal appears in the utilization circuit 41. The receiver shown in this modification may be readily utilized for receiving amplitude modulated 5 signals by merely changing the outputs of tubes C and D so that they are connected in parallel rather than in push-pull.

The receiver of Fig. 3a, like the receiver in Figure 3, includes all of the advantages of the receiv- 1o ers of Figures 1 and 2.

While the receiver of Figure 3a has been illustrated as utilizing a damped transmission line, it will be understood that in this receiver the transmission line L may be undamped, that is, 15 open-circuited or short-circuited. In this case the tap i0 is adjusted to a point on the line where Ythe reflected wave cancels the incident Wave and a receiver equivalent to the receiver of Figure 3 is obtained. 20

When undamped transmission lines L are used with the receivers of Figures 1, 2, 3 or 3a use is made of the fact that when incident and reflected waves form on the transmission line the point of minimum and of maximum of said waves 25 slides along the line as the input frequency is changed. Consequently when the frequency changes with signal modulation the tap is no longer on minimum point so that energy is passed to combining transformer T1 in the instance 30 of the undamped line arrangement of Fig. 3a, to oppose or add to the energy reaching the control electrodes of tubes C and D from transformer T2. These two amplitude modulated frequency modulation waves are detected and combined in 35' the transformer T4.

The above circuits show only the fundamental features of the present invention.

In most of these circuits the use of other elements is necessary in practice. For example, 40 volume controls, coupling tubes, and additional amplifiers may be added to the receivers in the appropriate places. Since the use of such elements will be obvious to those skilled in the art,' and for the sake of simplicity, suchelements have 45 been omitted from the present disclosure.

In the receivers in which a single detector is included, or in the receivers of the type shown in Figures 2, 3, and 3a, when one detector is switched olf the receiver has interference reduc- 50 ing properties of certain kinds of interference which are confined to one side of the wave.

Any of the receivers described above may 'in f accordance with the present invention, be used for the reception of phase modulation waves. This is accomplished by adjusting the circuits for frequency modulation as described above and using a correcting filter at the receiver which has its output voltages inversely proportional to its input frequency so that its characteristic is 00 as shown in Fig. 4, wherein audio frequency impressed on the input terminals of the correction circuit is plotted againstvoltage output.

When phase modulated. signals are received on a receiver arranged to receive frequency mod- 6.5 ulated signals, the inherent difference between the frequency and phase modulated signals causes the signal output of theafrequency modulated receiver to vary in amplitude directly as the frequency of the signal at the input of the 70 ceiver instead of being the same for all audio 75.

frequencies, as indicated by the dotted line of Fig. .5, would be directly proportional to the frquency of the signals impressed on the input of the receiver, as indicated by the full line of Fig. 5. In order to compensate for this distortion of the signal frequency when phase modulated signals are received on a frequency modulated signal receiver, a lter circuit or correction circuit, the amplitude of the signal frequency in the output of which is inversely proportional to the frequency of the signals impressed on the input of. the circuit, as indicated in Fig. 4 of the drawings, is utilized in accordance with the present invention to adapt a frequency modulated re- .ceiver for reception of phase modulated signals. The combination of the effect of a filter circuit or `correction circuit having characteristics asillustrated by Figure 4 with the effect of the inherent characteristics of a frequency modulated receiver on-phase modulated signals gives `an over-all characteristic such as indicated by the dotted line of Fig. 5, which is a true reproduction ofthe signal wave applied as phase modulation to the carrier at -the transmitter.

If a correction lter is used with the receiver to enable it to receive and properlyV translate phase modulated waves it may be connected at a point following the detector, as will be pointed out in more detail hereinafter.

Various formsof lter or correction circuits, which will affect the signal frequencies passed therethrough in such a manner as to make the amplitude of the signals at the outputvtheref inversely proportional to the frequency of the sigrected are applied to the primary winding of a,

" 4d transformer 5|l'and are impressed from the secondary. winding of said transformer to the input. electrodes 52, 54 of a thermionic tube 5| to energize the same in such a manner as to apply the necessary distortion for corrective effect to the signals relayed thereby. The control electrode 52 of tube 5| is maintained at the desired operating potential by means of a biasing source 55. The anode electrode 56 of tube 5| is connected through a. parallel circuit comprising a resistance 51 and capacity 58 to the cathode 54 by way of a high potential charging source 59. The low frequencies of the signal potentials are emphasized by means of the capacity 58 connected across the resistor 51. The impedance of this re- 55 sistance 51 and capacity C1 in parallel is high atthe lower signal frequencies and low at the higher signal frequencies. The amplification facto of the' tube 5|, which depends upon the external impedance of its anodecathode circuit, will be 60 high at the lower signal frequencies and vlow at the higher signal frequencies. The signal frequency oscillations appearing on the anode of tube 5| are impressed therefrom by way Qf a coupling condenser 60 to the control grid 5| vof a,

der to operate 62 at the desired point on its characteristic curve, biasing potential is supplied from the source 66 by way of. resistance 61 to the control electrodes '6| of tube 52. v

75 If the single distortion or correctiontube 5| 'nals applied to the input, may be used. -Several thereon in likemanner so that no corrective efdoes; not effect suiiicient distortion or correction of the signal frequencies passed therethrough, a second tube, connected, in circuit and operated similar to tube 5|,' may be connected in cascade with 5| to apply more distortion or corrective ef- 5 fect to the signal. y

In Fig.l 7 the signals to 'be corrected are impressed cn the input winding of a transformer 50 and utilized lfrom the secondary winding of transformer 63 in the same manner as in the arrangement of Fig. 6. In Fig. '1, however,no amplifieris shown connectedwith the correction tube 5|, although it is understood that the correctedsignals can be further amplified, if necessary, by connecting the output of tube 5| with the input of a thermionic amplifier. 'I'he secondary winding of the transformer 50 is connected in parallel with the potentiometer resistance 10 in order that the desired signal amplitude may be impressed on the input electrode 52 by way of the tap 1|. In this' arrangement the resistance R'z is of such a high impedance to the signal current as compared to the'impedance of the capacity Cz to the signal .current that the current passed through the circuits R2, C2 is governed mainly by the resistance of R2. This makes the current through the circuit elements Cz, Rz constant With frequency so that the voltage across C2 Will be inversely proportional to the frequency of the applied signal due to the fact 30 that the impedance of the condenser Ca varies 4inversely as the frequency of the signals applied across the terminals thereof vary.The potentials appearing at the terminals of C2 are impressed on the input electrodes 52, 54 of -correc'- tion tube 5|.

In the arrangement shown. in Fig. 'la correction is applied to the signal in the same manner in which correction is applied` thereto by the arrangement shown in Fig'. 7 However, in Fig. '1a a second tube 5|' is added for -the purpose of varying the amount of distortion or corrective effect applied to the signal frequency relayed therethrough. When tube 5| is switched-01T full correction will be obtained by means of the tube 5| in the same manner in which correction is obtained in the arrangement of 7. With the tube 5|' turned on signal potentials, the amplitude of -which may be determined by the tap 1|', will'be applied from the'parallel res-istancelll' to the terminals of the resistance R4 by way ofresistance R3. The resistances Rs, R4 will affect all of thefrequencies of the signal impressed fect will be applied to the signal appearing on the input electrodes 52 o`f the tube 5|?. Consequently, the oscillations at signal frequency, ap-l pearing on the anode 56 of tube 5| and applied therefrom to the transformer 64, will be the same for all 'frequencies and will represent in a normal 'manner the signal potentials applied at the input of the correction circuit. By moving the taps 1| -cross between frequency and phase modulated signal.l Furthermore, such. an arrangement is especially desirable .where a correction circuit of this type is used in the signal amplifier circuits of the transmitter and a second correction circuit of this type is used subsequent to the detector in the receiver receiving signals from said transmittel'.

I n the arrangement shown in Fig. 8, as in the prior arrangements, the signals to be corrected are impressed on the transformer 50 and the co'rrected signals are utilized from the transformer 64. In this arrangement, however, a different means is provided for emphasizing the lower frequencies of the signal. The value of the inductance I in series with the control electrode is so chosen that its impedance to the signal frequency is high as compared to the impedance of the resistance R5 to the signal frequencies. The inductance I then is the governing factor of the circuit and determines the intensity of the current passed through the circuits I, R5. Since the inductance I offers a higher impedance to the higher frequencies than to the lower frequencies, the current passing through the inductance I will be inversely proportional to the frequency of the impressed signals. Consequently. the voltages at signal frequency, appearing across the resistance R5, which are fed to thev control electrode 52 of tube 5|, will be inversely proportional to the frequency of the impressed signals. 1

In Figs. 9 and 9a has been shown an arrangement in which, by means of a novel circuit, a corrective effect, which is the converse of the manner in which phase modulated signals are distorted in a frequency modulated receiver, is applied to the signals. The distortion of the signal wave discussed hereinbefore is 'created by virtue of the fact that phase modulated waves are being received on a frequency modulated signal receiver. On the other hand, if a circuit is set up which receives frequency modulation on a phase modulation receiver, a distortion is created which is the inverse of the undesired distortion obtained when phase modulation is received on a frequency modulation receiver. Obviously, if the phase modulated signal is passed through these circuits in sequence the distortion effects, which are the inverse of each other, will add or cooperate to give a resultant signal which is truly representative of the initial signal to be -modulation receiver PMR as shown in Fig. 9.

'I'he logical assumption may be that, since a phase modulated signal receiver is used in this correction circuit, the phase modulations should be received directly on that unit. Howeverxthere are at least two reasons for following the present course. First, the received` signal output 7from phase modulated signals received on a frequency` receiver, including correcting means as illustrated in Figs. 6, '7, 7a, and 8, is different from that received directly on a phase modulation receiver with respect to interference, fading, and tuning characteristics. Consequently, a corrected frequency modulation receiver (receiving phase -modulated signals) will feed a certain circuitv more suitably than a phase modulation receiver receiving the same signals directly. Second. the

phase modulation system, including the local frequency modulation transmitter, when used for a correction circuit, in accordance with the present invention, is far more simplified than when the transmitter and receiver are at widely separated points. This may be realized by an inspection of the circuit of Fig. 9a, which shows a correction circuit of this type in detail.

In this arrangement the signal frequencies to be corrected are applied from the detector of a frequency modulation receiver tuned to a phase modulated signal to the input terminals of a transformer 50, the secondary winding of which is connected to the control electrode 90 of an oscillation generator 9| of the dynatron type. The anode 92 is connected with an oscillatory circuit 93 in which oscillations at high frequency are developed by producing a negative resistance effect in the anode cathode circuit, as disclosed more in detail in United States Patent No. 2,- 085,739, issued July 6, 1937 to M. G. Crosby. The high frequencies which are modulated in frequency, as disclosed more in detail in the above identified application, are impressed from the circuit 93 on to a winding 94, and from winding 94 in opposition to the control electrodes 95 and 96 of thermionic differential detectors 98 and |00 of a phase modulation receiver. The anodes |0| and |02 of differential detectors 98 and |00 are connected in series through resistances ||0 and I, as shown. Charging potential for the anodes is supplied from a source |03 connected between the terminals of resistances ||0 and I|| and the cathodes of tubes 98 and |00. The differential currents resulting from the signal frequencies impressed oppositely to the control electrodes of tubes 98 and |00 flow in the resistances I|0 and III. These differential currents are applied from the high potential terminals of resistances I |0and Il to the input terminals of a radio filter circuit comprising series inductances I, I' and parallel condensers C4 connected as indicated. After passing through the filter circuits I', C4 the differential currents ilow through resistances Rs, Rc to the control electrode |05 and cathode |06 of a second dynatron oscillation generator |88. Capacities C5 are connected between the terminals of the resistances R5, Re and ground. These resistances and 'capacities regulate and determine the time contact of the circuit interposed between the differential resistors 0, and the input electrodes of theoscillation generator |08 to regulate the sensitivity and rapidity of the control effect of the differential currents on the oscillator |08. A source |09 supplies direct current biasing potential to the grid electrode of |08. The diierential currents from resistances ||0 and are superposed on this direct current potential. The output circuit ||2 of the dynatrqn oscillation generator and modulator |08 is coupled through a link circuit ||3 with a transformer Ill, the secondary winding ||5 of which is connected in series with the control electrodes and 96 of differential detectors 98 and |00 so that the carrier frequencies developed in ||2 and modulated by the differential currents in |08 are applied cophasally to the control electrodes of the differential detectors 98 and |00. This entire arrangement of the differential detectors and the frequency control means for the supplemental modulator and generator |08 is, in many respects, similar to the automatic frequency control device disclosed in United States Patent No. 2,065,565 issued Dec. 29, 1926, to M. G.'Crosby The detected signals appearing in the anodes of differlio ential detectors 98 and |00 are applied by way oi' coupling. condensers I I6 and.I I1 to the terminals of series resistances IIS, IIS and from the terminals of said resistances to the control electrodes of a pair of amplier tubes |20 and I2 I hav' ing their anodes connected through the'prim'ary winding 63 of a transformer 64'. This phase modulation receiver, including the differential detectors 98 and |00, the frequency controlled os.

cillator means |08; and the repeaters |20 and I2I, impart to the signals, which niodulatethe frequency of the carrier impressed thereon, a-

distortion which is the converse of the distortion given to the phase modulated signal in the frequency modulated receiver. The two distortion effects add to provide in the output of vtransformer 64' a signal which is truly representative of the signal impressed on the original phase modulated wave. The corrected signal frequencies may be utilized from the secondary winding 65' of'thls transformer.

Any one of the correction circuits illustrated in Figs. 6, 7, 7a, 8, 9, and 9a, may be .utilized u ritl'il the frequency modulated receivers of Figs. 1, 2, 3,

Aand 3a, as indicated in Fig. 10, in which l is the aerial system, 2 is a signal amplifier of'any type, .and 8 0 indicates anyone 4of the phase or frequency or amplitude receivers of Figs. 1, 2, v3,' and 3a connected to 2 by Way of leads 3 and 5. The correction circuits of Figs. 6, '7, 7a, 8, 9, and 9a may be incorporated in the receivers by merely connecting the. primary winding of the transformer 50 of any of the correction circuits to the output terminals of the detectors R,' TAB, or'CD of the receivers of Figs. 1, 2,; 3, and 3a respectively.

When the receivers are so modified phase modulated signalsmay be received thereon Without distortion.

It will be obvious to the reader that the present invention is of particular importanceforseveral reasons. Many frequency .modulated `receivers of various types are in use today.' These receivers may, asfdescribed a`bove, be utilized to give undistorted phase modulation reception by fmerely connecting therewith a correctionf circuit as, disclosed above. Further, such `a receiving system as disclosed above also lends itself -admirably to diversity reception systems, as indicated in Fig. 11.

In Fig. 11 a plurality of aerial systems, X,"'Y,`

and 'Z may be coupled through radio'frequency amplifiers X1, Y1, and Z1.to the amplier and/or combining unit indicated diagrammatically at 2. The units X1, Y1, and Z1 may `be heterodyne receivers which reduce the signals to an intery mediate frequency for transmission over the lines to the unit 2.- The unit 2 may include'the radio frequency amplifiers or a`heterodyne receiver in addition to the combining unit.- The output. of

the unit 2 is, as indicated, connected by way of leads 3 and 5 to frequency or phase or amplitude modulated-signal receiver 80 of the type shown in any of the Figures l, 2, 3,'and 3a.

When the unit 80 includes a frequency modula-vv tion receiver, acorrection'circuit, as illustrated in Figs. 6. 7, 7a, 8, 9, or 9u, may be included in the unit 8 I 'shown dotted between the receiver 80 and the output jack.

' Furthermore it will be' obvious that the present invention is especially applicable to diversity receiver systems in which automatic volume cori- Atrol for theA radio frequency amplierscis provided. Such a system their might take the form of the arrangement disclosed diagrammatically in Fig. lla. In this arrangement a direct current component is derived 'from the output of the demodulation tube or rectier in 2 and. fed back to the radio frequency amplifiers of the units X1, Y1, and Z1 where itis used to-determine the biasing potential applied to the ftubes therein-l thereby determining the amplification fact'or of -the tubes. The arrangement is such that the desiredv relation between received signal strength and biasing potential may be maintained. A more complete understanding of the details of this volume control may be had by'referring to Moore U. S. Patent #1,849,632,and Crosby U. S.

A,Patent #1,835,761'. y

Although in the' arrangements of the present invention, asillustrated above, in general tubes of the triode type, except for the dynatrons of Figs. 9 and 9a.; are used, it will be understood that said circuits may obviously'be' modifled to. use 'any of the types of tubes in general use today. For example, tubes of the screen grid type may-be inserted in place of the triodes illustrated without departing from the spirit of the present invention. Furthermore, Yother tubes -also may be utilized, the.J only provision being that the tubes have the desired operating characteristics.

i Having thus described my invention and the operation thereof, what I claim is:

1. A frequency modulated signer receiving means comprising, signal -absorbing means, sig' nal amplifying means connected therewith, thermionic detecting means comprising a pair of thermionic tubes having their input electrodes connected in symmetrical circuits, a plurality of transmission channelsreach connected with the output circuit of said amplifying means, at

A least one of said transmission channels Vhaving an electrical length greater than'the electrical length of the other channels, which electrical length varies as the frequency-of the signals impressed thereon, means for coupling the output circuit of one. of said transmission channels in opposition to like control electrodes of said tubes, and- 'means for. coupling the output of another of said transmission channels co-phasally to like control electrodes of said tubes.

2. A frequency, modulated signal receivingmeans comprising, signal absorbing means, sig- 'nal amplifying means connected therewith, thermionic detecting means comprising a pair of thermionic tubes -having' their input electrodes connected. in symmetrical circuits, a plurality of transmission channels each connected with the output circuit of said amplifying means, at

signals into frequency and phase modulated signalswhich are characteristic ofthe frequency modulated signals and changingth'e phase modulated signals into characteristic amplitude mqdulated signals comprising, signal responsive means,

rectifying means comprisinga pair of thermionic tubes havingtheir input electrodes connected insymmetrical circuits,` a plurality of transmission channels each connected with the output circuit of said signal #responsive means, at least onel of said transmission channels having an electrical length greater than the electrical length of the other channels, which electrical length varies as the frequency of the signals impressed thereon, means for coupling the output circuit of said one transmission channel in opposition to the control electrodes of said tubes, and means for coupling another of said transmission channels cophasally to the control electrodes of said tubes.

4. Means for demodulating high frequency oscillations modulated in frequency at signal frequency comprising, signal receiving means, de

modulating means, a plurality of transmission channels coupled to said receiving means on the one hand and to said demodulating means, on the other hand, said transmission channels each terminating in thermionic tubes coupled to said demodulating means, said transmission channels being of different electrical length, one of said transmission channels comprising series inductances and parallel capacities of such value as to insure that the phase of the oscillations reaching the thermionic coupling tube at the terminal of said channel shifts in a manner characteristic of the changes in frequency of the received signal, and the ratio of the input to output amplitudes of the band passed by said channel is constant another of said channels having a small reactance whereby said oscillations reaching the thermionic coupling tube at the terminal of said channel are of substantially the same phase and frequency as the oscillations at the input of said channel.

5. A receiver for receiving desired signals transmitted as frequency modulations of a carrier wave comprising means for picking up a carrier wave modulated in frequency in accordance with a desired signal, means for heterodyning the picked up Waves to a band of intermediate frequencies, a rst coupling means for feeding a portion of the heterodyned waves including the intermediate carrier and all side frequencies to a rectifier, a second coupling means arranged to feed another portion of the heterodyned waves including the intermediate carrier and all side frequencies to said rectifier, each of said coupling means 'being arranged to transmit therethrough to said rectifier the mid-frequency or intermediate carrier of the heterodyned band of frequencies undiminished in` value with respect to and having avalue atleast as great as the side frequencies of the intermediate frequency band, only one of said coupling means introducing a phase shift, which phase shift varies with the frequency of the waves fed therethrough to said rectifier, whereby said rectifier is enabled to rectify amplitude variations of the resultant of said waves brought about by the combination of the phase shifted energies passed through said one coupling means and the relatively unshifted waves passed through the other coupling means.

6. In a system for demodulating oscillations modulated in length in accordance with signals, signal collecting means, thermionic rectifying means, a plurality of transmission channels of different effective electrical length, each having an input terminal coupled to said collecting means and each having an output terminal connected with the input electrodes of a thermionic coupling tube, there being a coupling tube for each channel and a circuit coupling the output electrodes of all of said thermionic tubes to said rectifying means. one of said transmission channels comprising series inductances and parallel capacities so related and Selected that the electrical length of said channel varies as the length of the applied oscillations vary.

7. A radio receiver for receiving and translating a frequency modulated carrier wave of substantially constant amplitude comprising, a pair of rectifier systemshaving input and output electrodes, means for feeding energy of carrier Wave frequency and energy of side band .frequencies derived from the received frequency modulated wave through a transformer in phase opposition to like input electrodes of said rectifier systems, said feeding means passing energy of carrier `wave frequency in p hase opposition to said like electrodes undiminished in amplitude relative to the amplitude of energy of side band frequencies fed thereto, and additional means for feeding received wave energy of substantially all frequencies including side band frequencies and wave energy of carrier wave frequency undiminished in strength relative to the strength of the side frequencies, in relatively phase displaced relation, with respect to the energy passed by said rst feeding means, and in push-push through a point electrically intermediate the enc.; of the secondary of said transformer to said lize input electrodes and means for connecting the output electrodes of said rectifier systen1r in phase opposition.

8. A radio receiver for receiving and translating a modulated carrier wave of substantially constant amplitude comprising a pair of rectifiers having their cathodes connected together and their anodes connected in phase opposition, means for feeding waveenergy derived from the carrier and its side .bands through a transformer in phase opposition to like control electrodes of said rectifiers, said feeding means passing energy of carrier wave frequency in phase opposition to said like electrodes undiminished in amplitude relative to the amplitude of side band energy fed thereto, and additional means for feeding received wave energy of all frequencies including side band frequencies and carrier Wave frequency undiminished in form, in relatively phase displaced relation, with respect to the energy passed by said first feeding means, and in pushpush to like electrodes of said rectiers.

9. A receiver for receiving and' translating carrier frequency waves of constant amplitude modulated in accordance with a signal comprising a transmission linehaVing-inductance and capacity, means for impressing said carrier frequency waves on said line, a pair of detectors each having an anode, a cathode and a control electrode, means connecting said cathodes together, means connecting said anodes in phase opposition, and means effectively coupling said control electrodes to points on said line Whereat the voltages of said impressed waves are displaced in phase.

10. A receiver for receiving -.nd translating carrier frequency Waves of constant amplitude modulated` in frequency in accordance with a signal comprising a transmission line of substantial electrical length having inductance and capacity, meansfor impressing said carrier frequency waves on said line, a pair of detector systems each having an input electrode and an output electrode, means connecting said output elec- .trodes in phase opposition, and means effectively coupling said inputelectrodes to different points on said line Whereat the voltages of said Waves impressed thereon are not in phase.

11. A receiver for receiving and translating waves which are frequency modulated in accordance with a desired signal comprising means for picking up waves so frequency modulated;

a pair of rectier systems each having an input electrode and an output electrode; means connecting said output electrodes in phase opposition; means, including a transformer having a primary winding connected to said pick-up means and a secondary winding connecting said input electrodes in phase opposition, operating to apply frequencymodulated waves of substantially constant amplitude and of a phase which varies as the frequency of the received waves vary to said input electrodes in phase opposition and means connected to said pick-up means for applying through a tap on said secondary winding,

frequency modulated waves of substantially unvaried phase and amplitude in push-pull relation to said input electrodes, whereby the resultant produced by the constant amplitude waves of varied and substantially unvaried phase is of variable amplitude and is rectified by said rectifier systems to produce the desired signal across the output electrodes of said rectifier systems.

12. In a modulated Wave demodulating means,

wave amplifying means, an output circuit coupled to said amplifying means, an undamped transmission line comprising series inductive reactances and parallel capacitive reactances, a

pair of thermionic tubes each having a control grid, a cathode and an anode, a connection between a point on said line and the cathodes of said tubes, a connection .between the control grid of one of said tubes and a point on said line at which the incident wave and reflected wave combine to increase their resultant, a connection between the control grid of the other of said tubes and a point on said line at which the incident wave and reflected wave combine to decreasetheir resultant, a circuit connected to the anodes and cathodes of said tubes, and signal utilizing means connected to said circuit.

13. A wave demodulating means as recited in claim 12 in which said last named circuit connects the anodes of said tubes in push-pull relation.

14. A demodulating means as recited in claim 12 in which said last named circuit connects the anodes of said tubes in parallel.

15. The method of demodulating frequency modulated electrical waves by means of a plurality of transmission media the electrical length of one of which varies in a manner characteristic of the variations in frequency of the modulations on the oscillations which includes the steps of,

setting up oscillations characteristic of said frequency modulated waves, passing all frequencies including the carrier frequency of said oscillations through each of said mediums, combining the energy passed through said mediums in phase displaced relation, and rectifying the combined energy to render the signal, said transmission media passing therethrough all frequencies including the carrier frequency without substantial attenuation so that said media have substantially flat amplitude versus frequency characteristics over the frequency range of the frequency modulations.

16. A'I'he method of demodulating frequency modulated electrical waves by means of a plurality of media the electrical length of one of which at least varies as the wave frequency varies to add to said variations additional variations in phase or frequency characteristic of the said signal frequency variations which includes the steps of, collecting said frequency modulated wave energy, passing a portion including the carrier and all side frequencies of said wave energy through each of said media, combining energy passed through said media in displacedyphase relation to .obtain wave energy the amplitude of 5 which varies in accordance with the signal frequency variations on said collected wa've energy, and rectifying the combined energy to render the signal, said media freely passing all received side frequencies and the carrier frequency there- 10 through.

17. A receiver for frequency modulated waves comprising means for picking up frequency modulated waves, means for heterodyning the picked up Waves t0 a convenient beat frequency. a pair 15 of detectors each having an anode, a cathode and a grid, the cathodes of said detectors being connected together, the anodes of said detectors .being connected in phase opposition, means lncluding a coupling transformer for feeding beat 20 frequency energy varying in phase as a function of frequency, in phase opposition to the control grids of said detectors, said coupling transformer passing all frequencies of the beat frequency energy including the carrier frequency in substan- 25 tially undiminished form, and means for feeding beat frequency energy between said cathodes and a point intermediate the ends of the secondary of said transformer coupling means for feeding waves of all frequencies in relatively undimin- 30 ished form in push-push to the control grids of said rectiers.

18. In a receiver for wave energy the frequency of which is modulated in accordance with a desired signal, means constituting a plurality of 35 paths for said signal frequency modulated waves, each of saidpaths having a substantially flat amplitude versus frequency characteristic there- .by freely passing the carrier frequency and all the other frequencies of the received band, means for receiving frequency modulated Waves including waves of carrier frequency and impressing them on said paths, a combination of reactance elements in one of said paths, and means for combining and rectifying wave energy including carrier frequency energy freely transmitted by and through each of said paths, said path containing the combination of reactance elements producing a change in phase at its output end, without substantial change in amplitude of the waves freely passed thereby, which change in phase varies in accordance with the changes in frequency of the waves applied to the input end of said path.

19. 'Ihe method of receiving a frequency mod- 55 ulated wave which consists in deriving from said Wave a plurality of currents each of said currents varying in frequency, an amount proportional to the amplitude and at a rate equal to the frequency of the transmitted signal, passing 60 the currents of varying frequency including the carrier frequency through two paths having different characteristics of transmission for said currents, one of said paths having a characteristic such that there is a greater phase shift at 65 its output end with variations in frequency applied to its input end than that produced at the output end of the other path with the same variations in frequency at its input, said paths attenuating the carrier frequency and side band frequencies substantially equal amounts and combining in a detector an output current from each path, each output current including substantially unattenuated carrier 'frequency and 75 10 side band frequency currents, to recreate the transmitted signal;

20. .The method of receiving a frequency mod-- ulated wave which consists in deriving from said wave a plurality of currents, each varying in frequency in accordance with the variations of the characteristic over a band of frequencies `so as to y freely pass to s aid detector, side band frequency wave energy and Wave energy of carrier frequency in unattenuated form relative to wave energy of side band frequencies.

2l. A receiver for'frequency modulated waves comprising means for picking up frequency modulated waves, means for heterodyning and linuting the 'picked up waves to a convenient, substantially constant amplitude variable frequency beat frequency, a pair pf detector systems each having an input and an output electrode, the output electrodes of said detector systems being connected in phase opposition, a first circuit including a transformer having its secondary coll connected in phase opposition to said input electrodes for feeding beat frequency energy in phase opposition to the said input electrodes, said circuit passing all frequencies of the beat frequency .energy including the carrier frequency without amplitude discrimination to said input electrodes but with a phase shift at the output end of said circuit which varies with the frequency of the waves applied to the input end thereof, and means for feeding frequency modulated beat frequency energy to a point effectively intermediate the ends o'f the secondary of said transformer thereby exciting said input electrodes cophasally with all frequencies of .the frequency modulated beat waves an amount which is substantially constant over the entire range of frequencies of the beat frequency, frequency modulated waves.

22. In a system for receiving wave energy the Wave length of which has; been modulated in accordance with voice signals to produce wave length modulated wave energy covering a predetermined band of frequencies and for converting saidwave length modulations to substantially corresponding vamplitude modulations of wave energy and demodulating the same,- means responsive'to wave length modulated wave energy, means coupled with said last named means for amplifying the wave length modulated wave energy, modulation potential utilizing means, amplitude modulated wave demodulating means having an input and having an output coupled to said modulation potential utilizing means, a rst coupling between said amplifier and said input of said demodulating means for impressing on said input, voltage output from said amplifier without appreciable shift of phase or variation in amplitude with respect to frequency within said band of frequencies, and a second coupling between said amplifier and said inp t of said demodulating means comprising reactance for impressing,

on said input, voltage output from said amplifier substantially without variation .of amplitude with respect to frequency within said band of frequencies but with a phase which varies with the ,frequency of.the received wave energy, said rst produce .a resultant varying in 'amplitude which resultant is demodulated by said demodulating means to reproduce said voice signals.

23. In a system for receiving wave,energy the length of which has been modulated in accordance with voice signals modulating the same,-

meahs'responsive to wavelength modulated wave energy, means coupled with said first named means for reducing the frequency of the wave length modulated wave energy, means coupled 'with said second named means for amplifying the wave length modulated wave energy of reduced frequency, modulation potential utilizing means, amplitude modulated wave demodulating means having an input and having an output coupled to said modulation potential utilizing means, a iirst coupling between said amplifier and said input of said demodulating means for impressing, on said input, voltage output from said amplifier subof variable amplitude which resultant is demodu-` lated by said demodulating means to reproduce said voice signals.

24. In a system for receiving and demodulating wave energy modulated in length or in amplitude in accordance with signalling potentials, a first demodulator of the electron discharge tube type having an input and having an output, a second demodulator of the electron discharge tube type having an input and an output, a first means coupling the inputs of said rst and second demodulators in phase opposition, means forim pressing said modulated Wave energy on saidilrstmeans to thereby excite said inputs in phase opposition by said wave energy, a second means coupling said inputs of said first and second demodulators in parallel or cophasal relationship, means for impressing said modulated wave energy on said second meansto thereby excite said inputsr cophasally by said wave energy, and a switch cooperating with the outputs of said first and sec-.

ond demodulators for coupling said outputs in phase opposition when said wave energy impressed on said first and second means is wave length modulated and for coupling' said outputs cophasally when said wave energy impressed on saldi` first second means lis amplitude modulated.

25. In a system for receiving and demodulating wave energy modulated in length or'in amplitude in accordance with signalling potentials, means for heterodyning said modulated wave energy to a lower frequency, a first demodulator of the electron discharge tube type having an input and having an output,'a second demodulator of the electron discharge tube type having an input and an output, a first means coupling the inputs of said first and second demodulators in phase opposition, means coupled to said heterodyning means for impressing said modulated wave energy of reduced frequency on said first means to. thereby excite said inputs in phase opposition by said Aerasure@ `means for impressing said modulated wave energy of reduced frequency on said second means to thereby excite said inputs cophasally by said wave energy of reduced frequency, and a switch cooperating with the outputs of said rst and second demodulators for couplingv said outputs in phase opposition when said waveenergy of reduced frequency impressed on said iirst and second means is wave length modulated and for coupling said outputs cophasaily when said wave energy 5 of reduced frequency impressed on said rst and second means is amplitude modulated.

MURRAY c. CROSBY. 

